Calcium (Ca2+) is a ubiquitous intracellular signal, which is responsible for controlling numerous cellular processes. This proposal focuses on understanding of Ca2+-homeostasis regulation using the power of C. elegans molecular genetics. This proposal is directed toward an investigation of functions and mechanisms of the intercellular Ca +-wave propagation and the store-operated Ca2+ (SOC) channels, which are part of the inositol 1,4,5-trisphosphate (IPS)-dependent pathway. The intercellular Ca2+-wave propagation is observed in a variety of cell types in many different species. It has been proposed that the intercellular Ca2+ waves function as synchronizing cellular activities in a particular organ. We first observed the intercellular Ca2+-wave propagation in C. elegans intestine, but its function is not known at all. Since intercellular Ca2+-wave propagation is a widely observed biological phenomena, this can be an important model system to investigate its mechanism and function using genetics. The SOC channels have an important function for Ca2+ uptake from the extracellular solution upon depletion of intracellular Ca2+ stores. It is speculated that the SOC influx has an important function for neural signaling and the pathogenesis of some neurodegenerative diseases: SOC influx may play an important role in the early development of Alzheimer's disease. Despite the biological and clinical importance of the SOC channels, their molecular identity is highly controversial. We will test the hypothesis that any transient receptor potential channels are responsible for the SOC activity in the C. elegans intestine. To study Ca2+ homeostasis, we developed a unique assay system by combining genetic, Ca2+-imaging, and electrophysiological approaches. This uniqueness of the system could contribute to revealing new aspects in the regulatory mechanisms of Ca2+ homeostasis, which were not able to be addressed well in other systems. Using this assay system, we will address the following three issues 1) investigating the function of the intercellular Ca2+-wave propagation, 2) identifying the store-operated Ca2+ channels using reverse genetics, and 3) isolation of mutations that affect Ca2+ homeostasis using forward genetics. The second and third aims will complement each other to identify important molecules for regulation of Ca2+ homeostasis. Completion of this project will provide new insights into human disorders that are caused by abnormal Ca2+ homeostasis.